1.0 Factual Information 1.1 The Accident The engine (CFM International [CFM]1 CFM56-5C4, serial number741-705) shut down without any warning given to the pilots or recorded by the centralized fault display system (CFDS).2 The flight crew contacted Cathay Pacific Airways technical personnel in Hong Kong, and, as a result of these discussions, the pilots decided to divert to Vancouver, British Columbia. There were no signs of engine compressor (N1) or turbine (N2) rotation from windmilling, leading the pilots to assess that the engine had seized. Therefore, they did not attempt to restart the engine. The operation of each of the four engines on the AirbusA340-300 is controlled by the full authority digital engine control (FADEC) system. The FADEC comprises many components, two of which are the electronic control unit (ECU) and the permanent magnet alternator (PMA). The ECU receives electrical power from the aircraft during the engine start sequence. Once the engine has attained sufficient speed, electrical power is provided by the PMA, which is driven by the engine accessory gearbox. Should the PMA fail at anytime during engine operation, the ECU, by design, acquires electrical power from another aircraft source. The number1 engine had accumulated 15527hours and 2622cycles before the shutdown. The accessory gearbox and the PMA itself had accumulated 15508 hours and 2619cycles. On the ground in Vancouver, maintenance personnel printed out a post-flight report from the CFDS. The report revealed no indication of the cause of the shutdown. They then examined the engine by borescope, verifying that the engine had not seized as the engine was rotated during the examination, and checked the accessory gearbox oil filter for contamination. No anomalies were detected. Maintenance personnel performed a non-motoring test to check the engine parameters and the ECU computer system. During this test, the N2 only reached 14percent rpm instead of the expected 28percent rpm. According to CFM, this lower-than-expected N2 speed is characteristic of a failure of either the PMA or the ECU. The PMA and the ECU computer were then removed. Maintenance personnel noted scoring and burning on the PMA rotor and stator and assessed excessive play in the drive shaft for the PMA rotor. Post-incident analysis shows that this indicates a potentially damaged drive shaft bearing. Maintenance personnel found neither the procedures for measuring or checking the play of this drive shaft nor any reference to rotor scoring in the approved aircraft maintenance or troubleshooting manuals. Cathay Pacific Airways technical support in Hong Kong were similarly unable to find any information on drive shaft play or rotor scoring. TSB investigators also did not find any pertinent information. The PMA and the ECU computer were replaced with serviceable units, and another non-motoring test was conducted. In this test, the N2 reached the required 28percent rpm. A full engine test run was carried out, but after about 10minutes, the engine shut itself down. As with the in-flight scenario, there were no advanced warnings or CFDS record of this shutdown. When the replacement PMA was removed and inspected, it showed scoring and burning similar to the original PMA. The entire PMA drive shaft assembly - comprising PMA rotor, roller bearing, drive shaft, ball bearing support, and ball bearing - was removed and examined. A visible crack was found in the ball bearing cage that supports the drive shaft where it exits the gearbox (seePhoto1). The crack could not be seen with the drive shaft assembly in place in the gearbox. A new drive shaft assembly and a third PMA were then installed, and another engine run was performed, this time without anomaly. The ECU (part number1851M42P06, serial numberECDN3879, software versionC.3.G) installed on the number1 engine at the time of the incident was subsequently sent to the component manufacturer for examination and test. No defects were identified, and the ECU was returned to the operator as a serviceable unit. The PMA drive shaft assembly was sent to CFM for examination and analysis. The CFM analysis of the failed ball bearing (part number305-100-410-0, serial numberUR06967) indicated that there was generalized spalling3 of the balls, wear on the cage pockets (including a fractured pocket), and sectorial spalling on 90 of the inner race (seephotos1and2). The ball bearing at this particular location is subject to temperatures as high as 160C, and it rotates at about 20 000 rpm. There was no indication of corrosion. The roller bearing (partnumber301-480-926-0) had two separate serial numbers on the races (inner race:UR31008, outer race:UR28466). No other anomalies were found on the remainder of the drive shaft components. The root cause of the spalling was not determined by CFM. The ball bearing had been the subject of CFM Service Bulletin (SB) 72-457, issued in July2001. The purpose of the SB was to force the introduction of the second source bearing (partnumber305-100-415-0, manufactured by SNFA) already available in the fleet and with a better service experience. This bearing replaced the bearing made by SNR Roulements (partnumber305-100-410-0), which was identified as an infant mortality4 issue. The SB applied to accessory gearboxes equipped with drive shaft bearings (partnumber305-100-410-0) and having accumulated less than 1500cycles, but applied to only 17individual CFM56-5Cengines. The serial number of the incident engine was not included in the 17engines prescribed in the SB; accordingly, the SB did not apply and the ball bearing had not been replaced. 1.2 Permanent Magnetic Alternator (PMA) Bearing Failures A search of the Transport Canada (TC) Service Difficulty Report (SDR) database did not reveal any malfunctions of either the PMA or the PMA drive shaft bearing. However, the CFM report of the failed bearing stated that there have been at least 26reported failures of the PMA drive shaft bearing, from a total of about 3400engines in the CFM56-5 series, which includes the Airbus A319, A320, A321, and A340 model aircraft. The CFM report revealed that bearings from two separate manufacturers have suffered similar types of failures. The CFM report indicated that there are two main contributors to the failure of the bearing: radial overload stress causing spalling on the inner race, and corrosion causing spalling on the outer race. This ball bearing unit is also used in other locations in the gearbox where no failures have been found or reported. CFM concluded that the incident ball bearing failed as a result of radial overload stress, which induced inner race spalling, the origin of which occurred 50to 70m in depth. Radial overload stress, also known as contactfatigue, results from two curved surfaces moving over each other in a rolling motion, as seen in a ball bearing over a raceway.5 The contact geometry and the motion of the rolling elements produce alternating subsurface shear stress, which accumulates and generates cracking. The cracking then propagates until a surface pit is formed and spalling results. If this degeneration continues, complete bearing failure occurs. Rolling contact components have a fatigue life, that is, a number of cycles to develop a noticeable fatigue spall. It should be noted that, unlike aircraft cycles, rolling contact cycles are 7to 10orders of magnitude greater. Rolling contact life typically involves cycle counts in the order of 106to 107before a noticeable fatigue spall develops. Correct and adequate lubrication of all bearings is essential for bearing life; oil delivery, temperature, and viscosity reduce wear and spalling, and increase fatigue life. The PMA drive shaft assembly was also examined and analyzed at the TSB regional wreckage examination facility. In particular, the TSB examination focused on indications of electrical arcing that had previously been documented as causing similar spalling on ball bearings. The TSB examination did not find any indication of electrical arcing, and the root cause of the spalling was not determined. TSB investigators determined that there is an extreme variation in the average total aircraft cycles before failure of the ball bearings due to spalling and other unknown causes. However, there is no direct correlation between these aircraft cycles and rolling contact fatigue cycles; the significant issue is the wide range of aircraft cycles before failure. Despite industry compliance with SB72-457, failures of the ball bearing continued regardless of part number or manufacturer. The TSB also determined that the accessory gearboxes for the AirbusA319, A320, and A321aircraft models, and the Boeing777 aircraft series, are manufactured by the same company, Hispano-Suiza. All of these aircraft types have experienced PMA drive shaft bearing failures. The roller bearing races are located at the opposite end of the drive shaft and are different than the ball bearings. These roller bearing races, previously identified as having different serial numbers for the inner and outer races, are normally a matched set, and according to CFM, the serial numbers for both races should be the same. The roller bearing did not exhibit any unusual wear characteristics and neither the TSB nor CFM determined if this serial number anomaly contributed to the failure of the ball bearing. It is noteworthy that previous ball bearing failures have occurred with correctly matched roller bearing races. The Airbus A340-300 is a fly-by-wire type of aircraft in which there are no conventional mechanical flight controls or engine controls; operation of the flight control surfaces and the engines by the pilots is routed through onboard computers. The exception is mechanical backup or control of the trimmable horizontal stabilizer and rudder. There is no provision for mechanical engine operation should the FADEC system fail. By design, the ECU automatically acquires electrical power from other aircraft sources when a PMA fails. A failure of the PMA is indicated on the cockpit CFDS. The U.S. Federal Aviation Administration (FAA), in Federal Aviation Regulation (FAR)33.28, and Canadian Aviation Regulations, Commercial Air Standards, Part V, Airworthiness Manual, Section 533.28, require, in part, that each engine control system that relies on electrical and electronic means for normal operation must interalia: (b) Be designed and constructed so that any failure of aircraft-supplied power or data will not result in an unacceptable change in power or thrust or prevent continued safe operation of the engine; (c) Be designed and constructed so that no single failure or malfunction, or probable combination of failures of electrical or electronic components of the control system, results in an unsafe condition; (e) Have all associated software designed and implemented to prevent errors that would result in an unacceptable loss of power or thrust, or other unsafe condition and have the method used to design and implement the software approved by the [Administrator/Minister]. Failure of the ECU to acquire electrical power from other aircraft sources during a PMA failure has caused in-flight shutdown (IFSD) events in several recent aircraft incidents. Notably these include Singapore Airlines (A340-May1999), Virgin Airlines (A340-May1999), and Ansett (A320-September1999). Further investigation by the TSB determined that the failure of the ECU to acquire other aircraft electrical power is not isolated to the AirbusA340 or to the CFM56-5Cengine. An FAA aviation safety report (number295661) reported an IFSD on an AirbusA320 caused by a faulty PMA. As recently as 14May2003, a Boeing777 equipped with two Rolls Royce Trent 800engines suffered a similar failure in flight and one engine shutdown. Synopsis The Cathay Pacific Airways AirbusA340-300 (CPA829), B-HXN, departed Toronto/LesterB. Pearson International Airport, Ontario, at 2352 eastern standard time on a scheduled flight to Hong Kong, with a planned refuelling stop in Anchorage, Alaska. There were 249passengers and 13crew members on board. One hour and nine minutes into the flight, while cruising at flight level350, the pilots felt an airframe vibration and observed the number1 engine shut down spontaneously. All cockpit indications leading up to the engine power loss were apparently normal. The pilots secured the number1 engine in accordance with the quick reference handbook, continued flight on three engines, and diverted to Vancouver International Airport, BritishColumbia. CPA829 landed at Vancouver at 0105 Pacific standard time without further incident. Ce rapport est galement disponible en franais. Minister of Public Works and Government Services 2004 Cat. No. TU3-5/3-2004E ISBN 0-662-38803-8 How This Report Is Organized A02P0261 Investigation Report Appendix Transportation Safety Board of Canada - AVIATION REPORTS - 2002 - A02P0261 Transportation Safety Board of Canada Main Links TSB Home Proactive Disclosure Marine Pipeline Rail Air Air Investigation Reports Recommendations and Assessments of Responses Board Concerns Air Statistics Reporting an Air Occurrence Air Investigation Reports Recommendations and Assessments of Responses Board Concerns Air Statistics Reporting an Air Occurrence